This invention relates to a fuel controller for an internal combustion engine. More particularly, it relates to a fuel controller which can stop the supply of fuel to an individual cylinder which is misfiring.
Electronic fuel injection systems for internal combustion engines of automobiles are becoming increasingly common. In these systems, an optimal air-fuel ratio is calculated by a microprocessor on the basis of various operating parameters such as the engine speed, the air intake rate, the air intake temperature, and the engine temperature. Electromagnetically-operated fuel injectors are then controlled so as to achieve an air-fuel mixture having the optimal air-fuel ratio.
Many automobiles are equipped with a catalytic converter for removing harmful components from the engine exhaust gases. A typical catalytic converter is a three-way catalytic converter which simultaneously oxidizes carbon monoxide and hydrocarbons while it reduces oxides of nitrogen (NOx). An electronic fuel injection system is usually designed to maintain the air-fuel ratio near the stoichiometric ratio so that the catalytic converter can function effectively.
Occasionally, due to breakage of parts, poor electrical connections, or equipment malfunctions, combustion does not take place properly in one or more cylinders of an engine and so-called "misfiring" occurs. Due to misfiring, a mixture of uncombusted fuel and air flows into the catalytic converter, and a sudden chemical reaction takes place, causing an enormous increase in the temperature of the catalytic converter. Under these conditions, the catalytic converter can not function properly, and harmful exhaust components are discharged into the atmosphere. The increase in temperature also produces degradation of the catalytic converter and shortens its life span. Furthermore, when the automobile is stationary, if dead grass or other combustible material should contact the catalytic converter when it is at an abnormally high temperature due to misfiring, there is the possibility of a fire starting.
To prevent such problems, various devices have been proposed for detecting misfiring and stopping the supply of fuel to an engine when misfiring takes place. For example, Japanese Published Unexamined Patent Application No. 63-63933 discloses an apparatus which detects misfiring by measuring the pressure inside the cylinders of an internal combustion engine. When it is determined that misfiring has occurred in a cylinder, the supply of fuel to all the fuel injectors of the engine is stopped.
U.S. Pat. No. 4,366,794 discloses a fuel injection control method in which misfiring is detected by comparing the voltage of the primary coil of an engine ignition coil with a predetermined value. If misfiring is detected, fuel injection is stopped by reducing the fuel injection quantity to zero.
However, in these and other conventional systems, even if only a single cylinder of the engine is misfiring, the fuel supply for all the cylinders is stopped, thereby stopping the engine. Therefore, the vehicle must be towed to a repair shop, even though the cylinders which were functioning normally were sufficient to enable the vehicle to run under its own power to the repair shop.